<!--
 * @Description: 
 * @Author: charles
 * @Date: 2021-11-09 11:14:33
 * @LastEditors: charles
 * @LastEditTime: 2021-11-09 12:07:42
-->
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>函数组件</title>
  <script src="https://cdn.bootcdn.net/ajax/libs/react/17.0.2/umd/react.development.min.js"></script>
  <script src="https://cdn.bootcdn.net/ajax/libs/react-dom/17.0.2/umd/react-dom.development.min.js"></script>
  <script src="https://cdn.bootcss.com/babel-standalone/6.26.0/babel.min.js"></script>
</head>
<body>
  <div id="app"></div>
  <script type="text/babel">
    const {useEffect,useState} = React; 
   
    function App(){
      const [num,setNum] = useState(0);

      useEffect(() => {
        setInterval(() => {
          setNum(num+1) 
        }, 3000);
      },['num']);

      return (
        <div>
          <h2>函数组件</h2>
          <div>数字 {num}</div>
        </div>
      )
    }
    ReactDOM.render(<App/>,document.getElementById('app'));



  </script>
</body>
</html>